Response of groundwater contamination hazard rating systems to variations in subsoil conditions beneath municipal solid waste (MSW) dumps in developing countries

Groundwater hazard rating systems are generally based on source-pathway-receptor approach. This study determines the response of rating system to the variations in subsurface conditions (generally designated as pathway component). Besides, the study also investigates the ability of the rating systems to respond to the changes in other components too (i.e., source and receptor components). For the purpose, three groups of sites with various combinations of site conditions, that may be encountered in the field, are employed, e.g., a smaller site located in sandy soil with receptors all around it using groundwater or a larger site having a thick clay layer underneath it and the receptors in vicinity using groundwater for drinking. For the analysis, four sets of corresponding rating scores are determined in this study from the selected eleven rating systems (ten earlier rating systems and mGW-HARS, a recently developed system). The investigation shows that mGW-HARAS performs the best for the three sets; for the remaining one set, the performance of mGW-HARAS is marginally lower than its predecessor, GW-HARAS. The sensitivity analysis of the selected rating systems with respect to four critical pathway parameters depicts that mGW-HARAS is sensitive to all the four parameters and has the highest sensitivity to soil permeability, i.e., 83% amongst all the selected rating systems. When these rating systems are applied to ten waste dumps from Indian cities, only one system, i.e., mGW-HARAS, is able to categorize these waste dumps in four hazard categories and responds suitably to the subsurface conditions encountered at these waste dumps.